During the early development of most animals, specific cells or groups of cells become committed to particular programs of development (determination). Although evidence indicates that the early commitments are dependent upon interaction between the zygotic nucleus and the maternally provided egg cytoplasm, the nature of the interaction is unknown. The goal of this proposal is to isolate and study a set of strict maternal effect lethal mutations in the nematode, Caenorhabditis elegans, based on the hypothesis that among these will be mutations that identify genes required for the proper functioning of the cytoplasmic components necessary for determination. To test this hypothesis, the C. elegans genome will be saturated for maternal effect lethal mutations. Using genetic analysis, genes that are strictly maternal in expression and whose products are required only for embryogenesis will be identified. Then, by a combination of light microscopy and time lapse video tape recording of the known cell lineages of C. elegans, and using morphological, histochemical, and immunological markers for specific cell types, these mutations will be further sorted to identify those that alter specific programs of development. The identification and characterization of a set of maternal effect lethal mutations that affect determination in C. elegans will provide necessary ground work for genetic, physiological, and molecular analyses to obtain information about the nature of determination, a crucial step in animal development.